1. Field of the Invention:
The present invention relates to a circuit arrangement comprising an amplifier, particularly a transimpedance amplifier, connected to an opto-electrical transducer, in which the gain of the amplifier is controllable with the assistance of a control element that modifies the load resistance of the amplifier.
2. Description of the Prior Art
A circuit arrangement of the general type set forth above is disclosed in German patent 32 04 839. This known circuit arrangement has a photo diode at the input and contains an iterative circuit composed of an emitter feedback branch between the output of the collector stage and the input of the emitter stage. The circuit arrangement composed of two stages forms what is referred to as a transimpedance amplifier that has a comparatively low input resistance and a comparatively extremely low output resistance. The drain-source path of a field effective transistor is connected in parallel to the collector resistor of the emitter stage, the resistance of the field effect transistor being continuously controllable with the assistance of a control voltage. The effective collector resistance can be varied within broad limits in this manner. A possibility of an external setting of the gain of the first amplifier stage within a relatively great dynamic range therefore derives. However, the d.c. operating point of the amplifier arrangement is thereby influenced by the gain control.
The known circuit arrangement should also comprise the standard requirements made in view of noise-optimized out-coupling of the electrical signals output by the photo receiver, of high gain and low power consumption, together with an optimally-low set noise.